1. The Field of the Invention
The present invention relates generally to lamination presses for forming resin products.
2. Background and Relevant Art
Laminated resin panels have a wide utility in design and architectural applications, including use as walls, partitions, lighting fixtures, displays, etc. Laminated resin materials are popular because they tend to be less expensive than materials such as glass or the like, in many applications where certain structural, optical, and aesthetic characteristics are desired. In addition, laminated resin materials tend to be more flexible in terms of manufacture and assembly, since resin materials are relatively easy to bend, mold, color, shape, cut, and modify in many different ways. One particularly popular technique is to embed decorative layers, such as, for example, fabrics, paper, colored films, printed images, or three-dimensional objects (grass, reed, rocks, flowers, metal, etc.) between translucent resin sheets. These and other resin panels are often produced using heated lamination, which involves the application of pressure and heat to at least partially melt the resin sheets to each other to form a final resin panel product.
Conventional lamination technology, however, can lead to panel damage or imperfections, and can introduce significant overhead and inefficiency into the resin panel production process, as explained in greater detail below. In many conventional lamination processes, a component press applies heat and pressure to a stack of sheets of material (often called a layup stack or laminate assembly, sandwich, or a book) to join the sheets together. A second component press then cools the sheets under pressure to form a resulting unitary product. In many lamination operations, it is necessary to control the pressing, heating, and cooling of the laminate assembly to ensure proper fusing and the minimization of flaws and stresses in the resulting product.
To press a laminate assembly together, conventional lamination presses typically use large, heavy cast iron platens. In particular, pistons, hydraulic cylinders, or apparatus act on finite contact points on platens to actuate and press the platens together. Pressure applied to finite contact points can bend, warp, or otherwise deform the platens over time. These imperfections can produce inconsistent pressure along the surface(s) of the laminate assembly, which often results in finished products having an inconsistent gauge, waves, or other deformities. Additionally, normal use can scratch, dent, or otherwise damage the surface of the platens, which can lead to similar corresponding surface damage in products formed by such platens.
One potential solution for damaged platens is to simply replace them. Unfortunately, the material, size, and construction of conventional platens make replacement extremely expensive and otherwise impracticable. Thus, manufacturers typically use tooling plates and/or pressure pads between the laminate assembly and the platens to compensate for any deformities in the platens. The tooling plates and pressure pads can help provide smooth surfaces and produce more uniform distribution of pressure across a laminate assembly. The use of tooling plates and pressure pads, however, also decreases the efficiency of the lamination processes and increases processing times. In particular, manufacturers must spend time and effort to position any tooling plates and pressures pads. Furthermore, the additional layers between the platens and laminate assembly reduce the heat transfer rate to the laminate assembly, and thus, require additional heat, time, and cost.
In addition to the foregoing, conventional pressing processes can create various drawbacks specific to the materials being processed. For example, when embedding three-dimensional objects within resin sheets, traditional pressing processes can smash or otherwise damage the three-dimensional objects. In particular, traditional presses can concentrate a disproportionate amount of pressure on a few of the three-dimensional objects as the resin sheets begin to melt, thereby producing a flawed final product. To avoid this, manufacturers often apply increasing amounts of heat and/or pressure in steps to help ensure the resin sheets melt and form around the three-dimensional objects instead of crushing them. Such stepped processes, however, can significantly increase processing times and overall process overhead.
In addition to the various drawbacks of conventional pressing processes, the heating processes of conventional lamination presses can also present various drawbacks and inefficiencies. Conventional presses typically heat the platens using either a plurality of electrical heating elements embedded within the platens, or by passing hot oil or steam through serpentine fluid channels formed in the platens. Each of these heating methods, however, can in some instances lead to hot spots and uneven heating.
Conventional platens are usually made of cast iron for its heat retention capabilities and for its manufacturability, which allows for the creation of the serpentine fluid channels and/or embedding of the heaters. The cast iron construction of the platens, however, tends to make precise temperature control difficult, requiring significant time and energy to heat or cool the platens to a desired temperature. For this reason, manufacturers often use a “hot” component press and a separate “cold” component press. The use of two component presses allows the manufacturer to maintain both presses at a desired temperature, and avoid the time and energy required to change the platen temperature.
The time and effort needed to transfer the laminate assembly from the hot component press to the cold component press, however, increases production time, creates the potential for damaging the materials, and otherwise adds inefficiency to the lamination process. Furthermore, in such cases the manufacturer will often maintain the heat of the hot component press for extended periods of time, even between jobs. Heating or maintaining the temperature of the hot component press between jobs, by itself, can lead to significant costs.
Even when using separate hot and cold presses, a manufacturer will often still need to adjust the temperature of a given hot or cold component press depending on the type and gauge of the material being processed. For example, if the manufacturer needs to process both ¼ inch and ½ inch gauge panels, the manufacturer may first adjust the temperature of the press for one gauge, such as the ¼ inch panels. After processing the ¼ inch panel, the manufacturer may then adjust the temperature for the ½ inch gauge panels. As mentioned previously, when using conventional lamination presses, such temperature adjustments tend to be difficult to determine and maintain with precision. Thus, if a site regularly processes a variety of different panel gauges or materials, the time and energy associated with these temperature adjustments can lead to significant manufacturing inefficiency.
Additionally, the cooling processes of conventional lamination processes can add even further inefficiencies and drawbacks to the lamination process. For example, conventional platens are often cooled by running cold liquids or air through the serpentine fluid channels formed in the platens. Uniform cooling of conventional platens can be problematic; however, because the introduction of low temperature cooling fluids into the fluid channels of the platens often cools the platen much faster at the inlet than the outlet. This can prevent the portion of the laminate assembly from properly cooling, require longer cooling time, or otherwise add inefficiencies to the lamination process.
Thus, conventional presses typically require significant front-end work, including a great deal of energy and labor. For example, typical cycles (combined pressing, heating, and cooling) for a given decorative resin panel using conventional lamination presses are in best case scenarios about thirty minutes or more. Such processing times do not include any time required to change the temperature of a press based on the material or gauge of the panel being processed. In addition, such operation cycles often require at least six to eight people.